Introduction
The National Airspace System (NAS) is the network of all components regarding airspace in the United States. This
comprehensive label includes air navigation facilities, equipment, services, airports or landing areas, aeronautical charts,
information/services, rules, regulations, procedures, technical information, manpower, and material. Many of these system
components are shared jointly with the military. To conform to international aviation standards, the United States adopted
the primary elements of the classification system developed by the International Civil Aviation Organization (ICAO). This
chapter provides a general discussion of airspace classification. Detailed information on the classification of airspace,
operating procedures, and restrictions is found in the Aeronautical Information Manual (AIM)
This handbook departs from the conventional norm, in that the airspace discussions are presented in reverse order, in
the belief that it is much easier to learn the airspace from least complicated to most complicated; also, the information
presented for basic visual flight rules (VFR) weather minimums is only that necessary for balloon operations. [Figure 5-1]
Other information, specifically for instrument flight rules (IFR) flying or night flight, has been omitted, as it has little
or no value to the balloon pilot. For a complete discussion of these issues, the balloon pilot should refer to the AIM, or
FAA-H-8083-25, Pilot’s Handbook of Aeronautical Knowledge.
Basic VFR Weather Minimums
Airspace
Flight visibility
Distance from clouds
Class G 1,200 feet or less above the surface 1 statute mile clear of clouds
(regardless of MSL altitude).
More than 1,200 feet above the 1 statute mile 1,000 feet above
surface but less than 10,000 feet MSL. 500 feet below
2,000 feet horizontal
Class E At or above 10,000 feet MSL 5 statute miles 1,000 feet above
1,000 feet below
1 statute mile horizontal
Less than 10,000 feet MSL 3 statute miles 1,000 feet above
500 feet below
2,000 feet horizontal
Class D 3 statute miles 1,000 feet above
500 feet below
2,000 feet horizontal
Class C 3 statute miles 1,000 feet above
500 feet below
2,000 feet horizontal
Class B 3 statute miles Clear of clouds
Class E
Class D
Class C
Class G
Class B
Figure 5-1. Basic weather minimums for balloon operations in the different classes of airspace.
Chapter 5: The National Airspace System
Airspace Classification
The two categories of airspace are regulatory and non-regulatory. Within these two categories, there are four types:
uncontrolled, controlled, special use, and other airspace. Figure 5-2 presents a profile view of the dimensions of various
classes of airspace. It will be helpful to refer to this figure as this chapter is studied, as well as remembering that almost all
sport balloon operations are conducted in Class E or G airspace.
14,500' MSL
Nontowered
airport with
instrument
approach
Nontowered
airport with
no instrument
approach
700'
AGL700'
AGL
18,000' MSL
FL 600
1,200'
AGL
700'
AGL
1,200'
AGL
1,200'
AGL
Class A
Class B
Class C
Class D
Class E
Class G
Class G Class G Class G
Figure 5-2. Dimensions of various classes of airspace
Uncontrolled Airspace
The following are kinds of uncontrolled airspace.
Class G Airspace
Class G or uncontrolled airspace is the portion of the airspace that has not been designated as Class A, B, C, D, or E. Class
G airspace extends from the surface to the base of the overlying Class E airspace. Although air traffic control (ATC) has no
authority or responsibility to control air traffic within Class G airspace, pilots should remember there are VFR minimums
which apply while operating in it. Class G airspace is essentially uncontrolled by ATC except when associated with a
temporary control tower. [Figure 5-2 and Figure 5-3]
Class G
Minimum Pilot Qualifications
VFR Visibility Minimum
VFR Minimum Distance from Clouds
Student certificate
1 statute mile
Clear of clouds
Figure 5-3. Class G airspace
In the eastern half of the United States, most Class G airspace is overlaid with Class E airspace, beginning at either 700
or 1,200 feet above ground level (AGL). In the western half of the United States, much of the Class G airspace goes up to
14,500 feet before the Class E airspace begins. The pilot is advised to consult the appropriate sectional chart to ensure that
they are aware of the airspace limits prior to flight in an unfamiliar area.
Most balloon operations are conducted in Class G airspace. There are no communications requirements to operate in Class
G airspace. If operations are conducted at an altitude of 1,200 feet or less AGL, the pilot must remain clear of clouds, and
there must be one statute mile of visibility. If the operations are conducted more than 1,200 feet AGL, but less than 10,000
feet mean sea level (MSL), visibility requirements remain at one statute mile, but cloud clearances are 1,000 feet above,
500 feet below, and 2,000 feet horizontally from any cloud(s). A popular mnemonic tool used to remember basic cloud
clearances is “C152,” a popular fixed-wing training aircraft. In this case, the mnemonic recalls, “Clouds 1,000, 500, and
2,000.”
Controlled Airspace
Controlled airspace is a generic term that covers the different classifications of airspace and defined dimensions within
which ATC service is provided in accordance with the airspace classification. Controlled airspace consists of:
• Class E.
• Class D.
• Class C.
• Class B.
• Class A.
Class E Airspace
Generally, if the airspace is not Class A, B, C, or D, and is controlled airspace, then it is Class E airspace. Class E airspace
extends upward from either the surface or a designated altitude to the overlying or adjacent controlled airspace. [Figure 5-2
and Figure 5-4] Also in this class are federal airways and airspace beginning at either 700 or 1,200 feet AGL used to
transition to and from the terminal or en route environment. Unless designated at a lower altitude, Class E airspace begins
at 14,500 MSL over the United States, including that airspace overlying the waters within 12 nautical miles (NM) of the
coast of the 48 contiguous states and Alaska, up to but not including 18,000 feet MSL, and the airspace above FL 600.
Class E
Minimum Pilot Qualifications
VFR Visibility Minimum
VFR Minimum Distance from Clouds
Student certificate
3 statute miles
500' below, 1,000' above,
2,000' horizontal
Figure 5-4. Class E airspace.
There are no specific communications requirements associated with Class E airspace; however, some Class E airspace
locations are designed to provide approaches for instrument approaches, and a pilot would be prudent to ensure that
appropriate communications are established when operating near those areas.
Visibility and cloud clearances for operations conducted in Class E airspace are similar to those of the Class G airspace. If
balloon operations are being conducted below 10,000 feet MSL, visibility is three statute miles and the basic VFR cloud
clearance requirements of 1,000 feet above, 500 feet below, and 2,000 feet horizontal (remember the C152 mnemonic).
Operations above 10,000 feet MSL require visibility of five statute miles and cloud clearance of 1,000 feet above, 1,000
feet below, and one statute mile horizontally.
Class D Airspace
Class D is that airspace from the surface to 2,500 feet AGL (but charted in MSL) surrounding those airports that have an
operational control tower. [ Figure 5-2 and Figure 5-5] The configuration of each Class D airspace area is individually
tailored. When instrument procedures are published, the airspace is normally designed to contain the procedures.
Class D
Entry Requirements
Minimum Pilot Qualifications
Two-Way Radio Communications
VFR Visibility Minimum
VFR Minimum Distance from Clouds
Prior two-way communications
Student certificate
Yes
3 statute miles
500' below,1,000' above,
2,000' horizontal
Figure 5-5. Class D airspace
Unless otherwise authorized, each aircraft must establish two-way radio communications with the ATC facility providing
air traffic services prior to entering the airspace and thereafter maintain those communications while in the airspace.
Balloon pilots approaching Class D airspace should call the ATC facility at a point where, if entry is denied, a safe
landing can still be executed. It is important to understand that if the controller responds to the initial radio call without
using the balloon’s call sign, radio communications have not been established, and the balloon may not enter the Class D
airspace. Many airports associated with Class D airspace do not operate on a 24-hour-a-day basis. When not in operation,
the airspace will normally revert to Class E or G airspace, with no communications requirements. In either case, balloon
pilots are reminded that, in the absence of an emergency situation, there is no absolute requirement to land at the airport
associated with the Class D airspace. In most cases, the first radio call will be made at a distance of five statute miles from
the airport.
Balloon pilots operating in the vicinity of an airport should exercise discretion. While balloons indeed have the right of
way over all powered aircraft as stated in Title 14 of the Code of Federal Regulations (14 CFR) part 91, section 91.113,
a pilot would cause less disruption by landing well short of the airport. This is nothing more than common courtesy and
common sense. The visibility requirement for Class D airspace is three statute miles; cloud clearances are the standard
VFR 1,000/500/2,000.
Class C Airspace
Class C airspace normally extends from the surface to 4,000 feet above the airport elevation surrounding those airports
having an operational control tower, that are serviced by a radar approach control, and with a certain number of IFR or
passenger operations. [ Figure 5-2 and Figure 5-6] This airspace is charted in feet MSL, and is generally of a five NM
radius surface area that extends from the surface to 4,000 feet above the airport elevation, and a 10 NM radius area that
extends from 1,200 feet to 4,000 feet above the airport elevation. There is also a noncharted outer area with a 20 NM radius,
which extends from the surface to 4,000 feet above the primary airport, and this area may include one or more satellite
airports. [Figure 5-7]
Class C
Entry Requirements
Minimum Pilot Qualifications
Two-Way Radio Communications
VFR Visibility Minimum
VFR Minimum Distance from Clouds
Prior two-way communications
Student certificate
Yes
3 statute miles
500' below,1,000' above,
2,000' horizontal
Figure 5-6. Class C airspace.
Figure 5-7. Example of Class C airspace on a sectional.
Balloon operations in Class C airspace, while technically feasible, are usually not advisable. To fly an aircraft in Class C
airspace requires not only a two-way radio to establish and maintain contact with ATC, but also an encoding transponder.
Very few balloons carry a transponder in normal operations. As a practical matter, under certain circumstances and with
prior coordination, it is possible to enter or depart Class C airspace without an operational transponder, but the practice is
generally discouraged. It is possible to fly in the vicinity of a Class C airport; for example, under the lower lateral limits of
the outer layer, without needing to penetrate the inner circle. Again, a balloon pilot is well advised to remain clear of the
controlled airspace, as a matter of common courtesy and good public relations.
Cloud clearances in Class C airspace are the same as Class D airspace: visibility of three statute miles and a distance from
clouds of 1,000/500/2,000.
Class B Airspace
Class B airspace is generally airspace from the surface to 10,000 feet MSL surrounding the nation’s busiest airports in
terms of airport operations. [ Figure 5-2 and Figure 5-8] The configuration of each Class B airspace area is individually
tailored, consists of a surface area and two or more layers (some Class B airspace areas resemble upside-down wedding
cakes). An ATC clearance is required for all aircraft to operate in the area, and all aircraft that are so cleared receive
separation services within the airspace.
Class B
Entry Requirements
Minimum Pilot Qualifications
Two-Way Radio Communications
VFR Visibility Minimum
VFR Minimum Distance from Clouds
ATC clearance
Private or student certification
Local restrictions apply
Yes
3 statute miles
Clear of clouds
Figure 5-8. Class B airspace.
As a general rule, balloons do not freely operate within Class B airspace. Equipment requirements are the same as for
Class C airspace; however, due to air traffic congestion, the balloon pilot requesting entry to Class B airspace will likely
be denied entry, as ballooning operations inside the Class B airspace constitute a potential traffic conflict. Most traffic
transiting the Class B airspace is being flown under an IFR flight plan, or, in the very least, provide a radar signature which
allows ATC to provide traffic separation. Due to their construction, balloons do not provide a radar return much larger than
a small flock of birds (and are frequently mistaken as such).
Should it become necessary for operational reasons to fly through Class B airspace, that flight should be coordinated at
least one hour prior, as provided for by 14 CFR section 91.215. It is permissible, and perfectly legal, to operate a balloon
under the lateral limits of the Class B airspace. Balloon pilots operating in the vicinity of Class B airspace are encouraged
to be familiar with the airspace, including visual ground reference points when conducting flight under the lateral limits to
avoid inadvertently encroaching on Class B airspace. Since aircraft operating in Class B airspace are under radar control,
there is a slight difference in the cloud clearance requirements. Visibility remains three statute miles, but the only cloud
clearance requirement is that the pilot remain clear of clouds.
Class A Airspace
Class A airspace is generally the airspace from 18,000 feet MSL up to and including FL 600, including the airspace
overlying the waters within 12 NM of the coast of the 48 contiguous states and Alaska. Unless otherwise authorized, all
operations in Class A airspace are conducted under IFR. For that reason, balloons do not utilize the Class A airspace, unless
operated on a waiver or are conducting some special operation, such as a record attempt.
Special Use Airspace
Special Use Airspace (or Special Area of Operation) is the designation for airspace in which certain activities must be
confined, or where limitations may be imposed on aircraft operations that are not part of those activities. Certain special
use airspace areas can create limitations on the mixed use of airspace. The special use airspace depicted on sectional charts
includes the area name or number, effective altitude, time and weather conditions of operation, the controlling agency, and
the chart panel location. On National Aeronautical Charting Group (NACG) sectional charts, this information is available
on one of the end panels.
Special use airspace usually consists of:
• Prohibited areas.
• Restricted areas.
• Warning areas.
• Military operation areas (MOAs).
• Alert areas.
• Controlled firing areas.
Prohibited Areas
Prohibited areas define airspace where the flight of civil aircraft cannot occur. Such areas exist for security or the national
welfare. Aeronautical charts show these areas with a “P” followed by a number (e.g., P-40).
Examples of prohibited areas could include Camp David and the National Mall in Washington, D.C., where the White
House and the Congressional buildings are located. [Figure 5-9]
Figure 5-9. An example of a prohibited area is Crawford, Texas.
Restricted Areas
Restricted areas contain activity hazardous to nonparticipating aircraft, and these areas may impose restrictions upon
aircraft operations not a part of the activity. Restricted areas denote the existence of unusual, often invisible, hazards to
aircraft (e.g., artillery firing, aerial gunnery, or guided missiles). Penetration of an active restricted area should not occur
without authorization from the controlling agency.
ATC facilities apply the following procedures:
1. If the restricted area is not active and has been released to the Federal Aviation Administration (FAA), the ATC
facility will allow the aircraft to operate in the restricted airspace without issuing specific clearance for it to do so.
2. If the restricted area is active and has not been released to the FAA, the ATC facility will issue a clearance which
will ensure the aircraft avoids the restricted airspace.
Restricted areas are charted with an “R” followed by a number (e.g., “R-4401”) and are depicted on the sectional charts.
[Figure 5-10] Restricted area information can be obtained on the back of the chart. [Figure 5-11]
Figure 5-10. Restricted areas on a sectional chart
Figure 5-11. Specific information about a restricted area can be found on the back of the sectional chart.
Warning Areas
Warning areas consist of airspace which may contain hazards to nonparticipating aircraft in international airspace. The
activities may be much the same as those for a restricted area. Warning areas are established beyond the three mile limit
and are depicted on aeronautical charts. Warning Areas are also defined on the backside of the appropriate sectional chart.
[Figure 5-11]
Military Operation Areas
Military operation areas (MOA) consist of airspace of defined vertical and lateral limits established for the purpose of
separating certain military training activity from IFR traffic. There is no restriction against a pilot operating VFR in these
areas; however, a pilot should be alert since training activities may include acrobatic and abrupt maneuvers. MOAs are
depicted by name and with defined boundaries on sectional, VFR terminal area, and en route low altitude charts and are
not numbered (e.g., “Camden Ridge MOA”). [Figure 5-12] However, the MOA is also further defined on the back of the
sectional chart with times of operation, altitudes affected, and the controlling agency. [Figure 5-13]